The automotive industry has actively sought improved emissions reduction, including reduction in emissions due to gasoline evaporation. When vapor pressure increases in the fuel tank due to conditions, such as higher ambient temperature or displacement of vapor during filling of the tank, fuel vapor flows through openings in the fuel tank. Some motor vehicles, due to increased emission standards, typically include a fuel vapor recovery system. To prevent fuel vapor loss into the atmosphere, the fuel vapor recovery system includes a vapor or purge canister for receiving fuel vapors generated in the fuel tank. A fuel vapor absorbent, typically activated charcoal, located in the vapor canister retains the fuel vapor when the vapors are displaced from the fuel tank during refilling. During operation of the engine, the fuel vapor contained in the vapor canister is purged by drawing fresh air through the canister and into the intake manifold of the engine.
Some fuel vapor recovery systems include a filtration device to filter the fresh air introduced into the canister during the purge operation. Filters that have been used include a foam filter placed in a container. However, water tends to pass through the foam filter and into the canister which reduces the effectiveness of the absorbent or charcoal. In addition, dust and/or other contaminants may build up on the foam filter and clog the filter, which further reduces its efficiency. In addition, some current filtration devices used in fuel vapor recovery systems may experience fluctuations in differential pressure, resulting in inefficient filtration of the fresh air introduced into the canister.
Therefore, it is desirable to have a low cost, low maintenance filtration device that does not require a complex, self-cleaning apparatus to filter the fresh air supplied to the vapor recovery canister. It is also desirable to have a filtration device that is configured to maintain a substantially constant differential pressure.